The goal of this observational study focuses on the effect of different preoperative anemia status on perioperative complications in patients under moderate- to high-risk surgery. Different anemia types conclude iron-deficiency anemia(IDA), anemia of chronic disease/anemia of inflammation(ACD/AI), and combined anemia.The main question it aims to answer is whether there is a difference in the incidence of complication related to oxygen supply and demand imbalance in patients with IDA, ACD/AI or combined anemia. Patients without preoperative anemia will be recruited as the control group for secondary outcome analysis, which is whether there is a difference in the incidence of complication related to oxygen supply and demand imbalance in patients with or without anemia.